1. Field of the Invention
The present invention relates to a catalyst characterization apparatus, and in particular to an improved catalyst characterization apparatus which is capable of more accurately characterizing surface properties of a catalyst by a volumetric method without exposing the catalyst in air, by combining a dynamic flow type chemical reactor with a volumetric type adsorption apparatus, performing a gaseous catalytic reaction, and characterizing the catalyst, alternately and/or continuously.
2. Description of the Conventional Art
In order to measure activity, selectivity, and deactivation of a heterogeneous catalyst, and understand a reaction mechanism thereof, it is necessary to characterize the catalytic properties such as an internal composition, a physical structure, and physical and chemical surface properties of a catalyst.
There are several methods for characterizing catalyst, such as a method of using an X-ray, a method of using an electron microscope, etc. A very important method for characterizing the catalyst uses an adsorption phenomenon on a catalyst surface. The method for characterizing catalyst using the adsorption phenomenon is classified into a volumetric type method and a dynamic flow type method.
The volumetric type catalyst characterization method is directed to measuring an adsorption balance of gas with respect to the catalyst surface and characterizing the catalyst, thus obtaining a relatively accurate characterization result. However, the measurement is time consuming, and the property of the catalyst may be varied during the preparation and pre-treatment process of a catalyst sample.
The dynamic flow type method for characterizing a catalyst is directed to a method of measuring the stage of non-equilibrium adsorption which varies dynamically, when gas flows through the catalytic layer. This method is simple compared to the volumetric type method, and the characterization time is shortened. However, since the measurement result is affected by the adsorption property of the catalyst and the operation condition, this method is less accurate compared with the volumetric type method.
The volumetric type adsorption apparatus which is used for the volumetric type method for characterizing a catalyst, as shown in FIG. 1, includes a manifold 1 connected to a standard volume tube 2, a sample tube 3, an adsorption gas and helium gas supply source 4, a vacuum pump 5, and through valves V1, V2, V3 and V4, respectively.
The standard volume tube 2 is a container used as a standard for measuring an internal volume. The container is filled with a liquid such as mercury, and then the internal volume is accurately measured before the container is attached to the apparatus. An absolute pressure gauge 6 is installed in the manifold 1.
The procedure of measuring an adsorption property of the catalyst using a volumetric adsorption apparatus will now be explained.
The standard volume tube valve V1 and the gas supply valve V3 are closed, and then the sample tube valve V2 and the vacuum pump valve V4 are opened. Thereafter, the vacuum pump 5 is operated by connecting the sample tube 3 to the vacuum pump 5 through the manifold 1, and then the sample tube 3 is ventilated. The sample tube valve V2 and the vacuum pump valve V4 are closed, and gas such as He which is regarded as an ideal gas from the adsorption gas and helium gas supply source 4 fills the standard volumetric tube 2 through the manifold 1. At this time, pressure P1 is measured by using an absolute pressure gauge 6. The standard volumetric tube valve V1 and the gas supply valve V3 are closed thereby to close the standard volumetric tube 2. The adsorption gas, an helium gas supply source 4 and then the vacuum pump valve V4 are opened, and the manifold 1 is ventilated by the vacuum pump 5. After the interior of the manifold 1 is vacuumized, the vacuum pump valve V4 is closed, and the standard volumetric tube valve V1 is opened, thus supplying gas from the standard volumetric tube 2 to the manifold 1. Afterwards a final equilibrium pressure P2 is measured by the absolute pressure gauge 6. The volume of the manifold 1 is obtained by using an interrelationship between the pressure and volume of the gas with respect to the pressures P1 and P2 based on Boyle's law. The standard volumetric tube valve V1 and the gas supply valve V3 are closed, the sample valve V2 and the vacuum pump valve V4 are opened, then the manifold 1 and the sample tube 3 are ventilated by the vacuum pump 5. The sample valve V2 and the vacuum pump valve V4 are closed, and the gas supply valve V3 is opened. Thereafter, gas such as helium from the gas supply source 4 fills the manifold 1, the gas supply valve V3 is closed, the pressure P3 is measured by the absolute pressure gauge 6, the sample tube valve V2 is opened, the gas from the manifold 1 is supplied to the sample tube 3, and the final equilibrium pressure P4 is measured. Thereafter, the volume (the volume excluding the catalyst) is obtained by using an interrelationship between the pressure and volume of the gas with respect to the pressures P3 and P4 based on Boyle's law.
Therefore, it is possible to measure the amount of gases adsorbed into the catalyst based on the equilibrium pressure differences between the equilibrium pressure when the gas was not adsorbed on the catalyst based on the pressure-volume interrelationship between the manifold 1 and the sample tube 3, and the equilibrium pressure when the gas is adsorbed on the sample.
In order to measure the surface area of the catalyst, the physical adsorption of nitrogen is performed, thus measuring a BET surface area, a volume of a pore, and a mean diameter of pores. In order to measure the surface area of a metal, the amount of chemical adsorption of hydrogen and CO which are selectively adsorbed into the metal surface is measured, and it is possible to measure the surface area of the metal of the catalyst surface and the mean size of metal particles.
In addition, as the catalyst characterization method using a dynamic flow type characterization apparatus, a gas pulse chemical adsorption method which is mainly used for measuring the surface area of a metal of a catalyst, and a temperature programmed desorption technique for studying an adsorption state of a gas adsorbed on the catalyst are generally used.
In the gas pulse chemical adsorption method, a supported metal catalyst is pre-treated in a reactor, and then the system is ventilated by using a vacuum pump. The adsorption gas is supplied to the reactor by a sample injection valve having a sample loop of a predetermined volume together with an inert carrier gas, which is then adsorbed into the catalytic layer. The pulse adsorption operation is repeated by the sample injection valve until the concentration of adsorption gas at the gas outlet of the reactor is constant, and the amount of chemically adsorbed gas is calculated based on the difference between the amount injected in a pulse form and the amount of gas measured at the outlet of the reactor.
The temperature programmed desorption (TPD) method which is one of the temperature programmed techniques is a non-equilibrium method, wherein a measured gas is adsorbed on a sample, and then the gas adsorbed thereon and/or desorbed therefrom is characterized by using a gas chromatograph or a mass spectrograph, with continuously increasing the temperature of the sample, thus studying the state of the chemical adsorption. As another technique among the temperature programmed techniques is a temperature programmed reduction (TPR) method which is directed to measuring the amount of hydrogen, which is consumed when continuously increasing the temperature using an inert gas containing hydrogen, with a thermal conductivity detector (TCD), a gas chromatometer, or a mass spectrograph, thus studying reduced catalyst. As still another method among the temperature programmed techniques, there is a temperature programmed surface reaction (TPSR) method which is directed to adsorbing a reactant on a catalyst surface and then studying the reaction mechanism based on the consumption rate of the reactant gas, or a production rate of the product when continuously increasing the temperature by using an inert gas containing another reactant gas.
In the conventional method, when characterizing catalyst by using a separate apparatus from the catalytic reactor, the catalytic property is often changed during the process of performing a required pre-treatment, i.e., after the catalyst used for a reaction is removed from the reactor and is moved to the apparatus for characterizing catalyst.
Therefore, in order to check the catalytic property during the reaction, the catalytic property must be characterized without removing the catalyst from the reactor, but in situ (in the reactor).
As a conventional apparatus for accomplishing this object, is a catalyst characterization apparatus combining a dynamic flow type reactor with a dynamic flow type characterization apparatus (hereinafter, referred to as a "dynamic flow type reaction dynamic flow type characterization apparatus"), and a catalyst characterization apparatus combining a batch type reactor with a volumetric type adsorption apparatus (hereinafter, referred to as a "batch type reaction volumetric flow type characterization apparatus").
The dynamic flow type reaction dynamic flow type characterization apparatus was proposed by Carberry et. al. (Appl. Catal., 19 (1985), 119-139), which is capable of characterizing a sample without exposing a sample in air. However, since the amount of chemical adsorption is varied in accordance with the adsorption property of a metal and the pulse period and flux of a gas, it is impossible to accurately measure the amount of chemical adsorption, thus lowering the reliability of the measurement.
The batch type reaction volumetric type characterization apparatus was proposed by Brunauer et. al. (J. Am. Chem. Soc. 60 (1938) 309), which is capable of obtaining comparatively accurate experimental data, but since almost all catalytic reaction is proceeded in the dynamic flow type reactor, it is difficult to apply the apparatus in the actual reaction.